This invention concerns nozzles for drilling tools which work rock by abrading or shearing it, e.g., a one-piece tool fitted with blades or cutting edges made of diamond, polycrystalline diamond compacts or PDC, tungsten carbide, etc.
These nozzles must possess good irrigation, cleaning, and blade-cooling and cutting edge-cooling properties, and must drain off debris effectively.
It is known that cylindrical or convergent nozzles give excellent performance as regards destruction of rock, since they concentrate the flow of irrigation fluid on a small section. They are used for this purpose in tools fitted with tricone bits.
In the case of one-piece tools, the most important factor is not that of the destruction of the rock by hydraulic impact, but rather that of a homogeneous irrigation of the entire functional surface of the tool. This result could certainly be achieved by fitting the one-piece tool with wide nozzles which produce wide-cross-section jets of fluid and which have the further advantage of not permitting clogging with rock debris; however, in the event that clogging, a rare but potential phenomenon, should occur, unclogging would prove difficult, since, in a wide nozzle, the loss of head or pressure drop is low. Should the tool incorporate several other wide, unclogged nozzles, there would not be enough discharge available to unblock the obstructed nozzle.
One solution used to facilitate the unclogging of the nozzles might involve the choice of nozzles having a small cross-section of flow, since the high loss of head would make it possible to effect the unclogging operation. However, in this case one encounters the problem that small cross-section nozzles clog easily.
U.S. Pat. No. 4,703,814 discloses nozzles capable of being mounted or detached from a drilling tool using an Allen wrench, which saves space and contributes a tightening torque higher than those in standard nozzles. However, these nozzles in no way solve the problem set forth above, i.e., that of allowing good irrigation, self-cleaning, and good cooling of the blades and cutting edges, as well as unclogging of the nozzles. U.S. Pat. No. 4,185,706 concerns the use of cavitation-effect nozzles designed to destroy rock by cavitation. Cavitation is a destructive phenomenon caused by mini-explosions which generate destructive shockwaves. However, these nozzles do not solve the problem forming the basis of the invention.
European patent application No. 146,252 relates to an assembly of components designed to produce a nozzle resistant to very high pressures. This nozzle does not, however, have a structure that would enable it to improve cleaning, the distribution of fluid, and cooling of the drilling tool.